The present invention relates generally to a method and apparatus for treating a tachycardia event in a medical device, and, more specifically, the present invention relates to adjusting delivery of anti-tachycardia pacing regimens in a medical device.
A typical pacemaker/cardioverter/defibrillator (PCD) device has the capability of providing a variety of anti-tachycardia pacing regimens. Normally, these regimens are applied according to a pre-programmed sequence, and each regimen includes a predetermined number of pacing pulses. After the series of pacing pulses is delivered, the device checks to determine whether the series of pulses was effective in terminating the detected tachycardia. Typically, termination is confirmed by a return to either a sinus rhythm or demand-paced rhythm, in which successive spontaneous depolarizations are separated by at least a defined interval. If the tachycardia is not terminated, the PCD device delivers a subsequent series of pacing pulses having modified pulse parameters, e.g. reduced inter-pulse intervals and/or an altered number of pulses. The typical PCD device bases future treatment on whether the tachycardia has been terminated by confirming a return to normal rhythm. Devices which function according to the basic methodology described above are disclosed in U.S. Pat. No. 4,830,006 issued to Haluska et al., U.S. Pat. No. 5,836,971 issued to Starkweather and U.S. Pat. No. 5,846,263 issued to Peterson et al.
Recent efforts have focused on modifying subsequent anti-tachycardia pacing regimens based on feedback received from previous anti-tachycardia pacing regimens. As described in U.S. Pat. No. 6,167,308 issued to DeGroot, if a PCD device determines that a particular pacing regimen, if continued, would likely not result in termination of the tachycardia, then either a new anti-tachycardia pacing regimen having modified pulse parameters is employed or the device delivers a high energy cardioversion pulse. To accomplish this result, the device first delivers a short series of pacing pulses at the defined parameters of the pacing pulse regimen, and then interrupts delivery of pacing pulses to await the next spontaneous depolarization and determine the return cycle length. The device then resumes delivery of the pacing pulse regimen for a second, greater number of pacing pulses, and again measures the return cycle length following the last pacing pulse. In the event that no increase in the return cycle occurs following the delivery of the longer series of pacing pulses, the device terminates the pacing pulse regimen presently underway, and initiates the next scheduled therapy, which may be a pacing pulse regimen, (preferably at a shorter inter-pulse interval) or a cardioversion shock. Pacing pulse regimens are a preferred first treatment method for tachycardias because cardioversion shocks are more uncomfortable for the patient and require a greater amount of energy.